Embodiments of the present invention relate to an arrangement to be used for retrieving a laydown head to a surface vessel from a pipeline end section that is secured to a pipeline termination skid at the seabed. The invention also relates to a system comprising such an arrangement and a method for retrieving a laydown head to a surface vessel from a pipeline end section that is secured to a pipeline termination skid at the seabed.
Development within offshore oil and gas exploration in the recent years has been directed to subsea installations for processing and transport of oil and gas. These subsea installations replace the traditional platforms, where oil and gas are transported up to the platform for further processing and transport. This development of subsea production, processing and transport systems has resulted in an increasing need for subsea connection arrangements for coupling together a longer pipeline installed on the seabed and a so-called “spool piece” without requiring any assistance of divers. A spool piece is used for connecting a pipeline termination to a pipe termination of a subsea installation, such as e.g. a subsea production manifold. The spool piece is designed to span between the end points of the pipeline termination and the pipe termination in order to complete a connection between the pipeline and the pipe. The spool piece is provided with a spool piece hub which shall mate with a corresponding pipeline hub arranged at the pipeline termination.
A pipeline termination skid to be mounted to a pipeline end section in order to support a pipeline hub of the pipeline end section during and after the connection of the pipeline hub to a corresponding spool piece hub is previously known from WO 2006/005994 A1. This known pipeline termination skid is so designed that a pipeline end section may be mounted thereto subsea by lowering the pipeline end section into a seat of one or more holding units of the pipeline termination skid and thereafter displacing the pipeline termination skid along the pipeline end section so that the respective seat is brought into engagement with an alignment element secured about the pipeline end section so as to thereby fix the pipeline end section axially and radially in relation to the pipeline termination skid. When the pipeline end section has been secured to the pipeline termination skid, a spool piece termination structure carrying the spool piece hub and a clamping device is connectable to the pipeline termination skid by being lowered into engagement therewith. After the landing of the spool piece termination structure on the pipeline termination skid, the actual connection of the pipeline hub to the spool piece hub may be performed by displacing the clamping device and the spool piece hub in relation to the pipeline termination skid and the pipeline hub so as to bring the pipeline hub and the spool piece hub into contact with each other, whereupon the clamping device is activated so as to clamp together the pipeline hub and the spool piece hub. When a pipeline termination skid of this type is used, the entire pipeline may be laid on the seabed before the pipeline end section is secured to the pipeline termination skid.
Before and during the connection of the pipeline end section to the pipeline termination skid, a tubular member in the form of a so-called laydown head is secured to the pipeline hub of the pipeline end section. The laydown head extends in line with the pipeline end section and may be provided with valves to make the laydown head capable of functioning as a pig launcher. As an alternative, the laydown head may lack such valves. During the connection of the pipeline end section to the pipeline termination skid, the pipeline end section may be lifted by means of wires fixed to the laydown head. When the pipeline end section has been secured to the pipeline termination skid, the laydown head is disconnected from the pipeline end section and retrieved to a surface vessel. A retrieval of a laydown head from a pipeline termination skid of the type disclosed in WO 2006/005994 A1 is normally accomplished be means of a lifting frame, which is lowered downwards onto the pipeline termination skid so as to bring the lifting frame to bear against the pipeline termination skid with a horizontal girder of the lifting frame positioned vertically above the laydown head, a number of chains being fixed to the girder at different positions along the length thereof. Thereafter, the lower end of each chain is fixed to the laydown head and the chains are stretched by means of ROV operated (ROV=Remotely Operated Vehicle) chain hoists, whereupon the laydown head is disconnected from the pipeline end section so as to become suspended by the girder through the chains. The lifting frame is then, by means of lifting wires, lifted upwards to a surface vessel with the laydown head hanging below the girder of the lifting frame through the chains. The retrieval of a laydown head by means of such a lifting frame is a rather complicated and time-consuming operation.